Adaptive Fixed-Time Fractional-Order Terminal Sliding Mode Controller for Autonomous Underwater Vehicle Under External Disturbances

This paper proposes an adaptive fixed-time fractional-order non-singular terminal sliding mode control (AFtFoNTSMC) strategy to enhance the trajectory tracking performance of autonomous underwater vehicles (AUVs) under external disturbances. A novel fractional-order non-singular terminal sliding mode (FoNTSM) control strategy was developed, which effectively resolves singularity problems and attenuates chattering. To compensate for unknown disturbances, a fractional-order adaptive law was developed, which enhances system robustness without requiring prior knowledge of disturbance bounds. Building upon fixed-time stability theory, the proposed controller ensures that tracking errors converge to equilibrium within a predetermined settling time, independent of initial conditions. Lyapunov stability analysis rigorously proved the system’s fixed-time stability and provided an upper bound for the convergence time. Comparative simulations demonstrated that the AFtFoNTSMC outperforms conventional methods in terms of tracking accuracy, chattering suppression, and disturbance rejection, validating its effectiveness and superiority.